Assessing the Impacts of Upland Land Cover on the Hydrology of Geographically Isolated Wetlands in the Southeastern Coastal Plain

Abstract

The southeastern coastal plain has experienced increasing water scarcity due to drought, climate and land-use change, and increasing populations. Geographically isolated wetlands (GIWs), a frequent component of coastal plain landscapes, provide valuable ecosystem services such as wildlife habitat, water storage, nutrient processing, and sediment retention. Although these wetlands are also vulnerable to water scarcity, they have generally been excluded from federal regulatory protections. Because of their small size and lack of continuous connectivity to other water bodies, GIW hydrologic factors like hydroperiod, depth, and volume are highly dependent on ecosystem processes in surrounding landscapes. Our goal was to link GIW hydrology to landscape variables such as forest structure and local geomorphology. First, we developed a simple field-based method to characterize GIW bathymetry using a low-cost Deeper Smart Sonar CHIRP 2+ fish finder, and we demonstrated the method in three seasonally inundated wetlands. This novel approach offers a quick and cost-effective way to obtain precise depth-area-volume relationships for small wetlands, allowing bathymetry-dependent hydrological processes, like evaporation, and ecosystem services, like groundwater recharge, to be more accurately quantified. Second, we defined catchment areas with topographic data and used water level and precipitation data to estimate water balance components for select GIWs. We found that water fluxes both entering and exiting the wetlands are impacted by the surrounding landscape and tested this relationship by analyzing the effects of Hurricane Michael on GIW hydrology, which showed that reduced upland vegetation density reduced wetland recession rate. Third, we modeled the hydrologic effects of longleaf pine restoration in the catchment areas of three GIWs using the Soil and Water Assessment Tool (SWAT), finding that replacing existing vegetation with low-density longleaf pine forests would increase water yield, theoretically leaving more available water for GIWs. We hope that these results contribute to a more comprehensive understanding of how geomorphological and landscape factors affect GIW hydrology, and aid in informing land management decisions in the catchment area of these GIWs.